WIT Breaking Change Check

Classifies every modification in the current WIT diff against the breaking-change taxonomy and reports a verdict for each finding.

When to Use

• Before merging any branch that touches wit/
• When reviewing a PR that modifies WIT interface definitions
• To verify a WIT change is safe before publishing a plugin-compatible release

Procedure

1. Run git diff origin/master -- wit/ to obtain the current diff.
2. For each wit/vN/ directory in the diff, check whether wit/vN/.frozen exists. If absent, report the version as experimental and state that components must be rebuilt against the WIT shipped by the target host; do not claim the frozen-version compatibility window applies.
3. For each frozen version with changes, classify every modification against the breaking-change taxonomy in wit/VERSIONING.md:
   • Breaking: removing/renaming any type, function, record field, enum case, or variant case; adding a case to an existing enum or variant; changing a function signature; changing a field type; reordering record fields; adding a required (non-optional) field to an existing record; adding a non-capability-gated required function to an existing interface.
   • Non-breaking: new flags bits, new capability-gated functions, new record/variant/enum types (but not cases added to an existing enum or variant), new interfaces, new worlds, @since/@unstable annotation additions.
4. Report each finding with a verdict:
   • ✅ Non-breaking — with a brief reason citing the taxonomy
   • ❌ Breaking — with a brief reason citing the taxonomy
   • ⚠️ Uncertain — with the ambiguity explained
5. If any breaking change is found, summarize the required migration path for plugin authors. For an unfrozen experimental version, state that components must be rebuilt against the target host's shipped WIT; the current-and-previous-major host compatibility window begins only after a version directory is frozen.

Notes

The .frozen marker is a human-readable convention: its presence signals to reviewers and this skill that the version is stable and requires the breaking-change check before merge. For experimental (unfrozen) versions, report the target-host rebuild requirement without assigning a frozen-version compatibility verdict.